Field of the Invention
The present invention relates to a projector, its control method, and an image projection system.
Description of the Related Art
In the past, as a projector (projection device) there has been known a projector which projects and displays images generated by a light valve such as a liquid crystal panel onto a screen. In addition, in recent years, enhancement of the resolution of images is progressing, and it is desired to display images of a large number of pixels such as, for example, 4K2K, 8K4K, or the like on a big screen. In general, in order to increase the number of pixels and the size of a projector, it is necessary to make finer the light valve such as the liquid crystal panel, etc., or to adopt a high-intensity light source, so that the costs will go up. For that reason, projection display with a large number of pixels and a big screen can often be carried out by means of multiple projections using a plurality of projectors each of which has an ordinary light valve and an ordinary light source, and hence is inexpensive.
The multiple projection is a projection method in which projection (projected) images produced by a plurality of projection devices are joined or combined with one another on a plane of projection (screen) so that one image as a whole is displayed. At the time of combining the plurality of projection images, their joints will be visually seen or discerned if their positions are not adjusted in a precise manner, thus giving rise to degradation in quality of the projected images. Therefore, processing to make the joints inconspicuous or unnoticeable, which is called edge blend, is used. In the edge blend processing, a plurality of projected images are combined with one another by being made to partially overlap with one another. Then, steps or differences in luminance between overlap areas and non-overlap areas of the projected images are made inconspicuous by carrying out light dimming or reduction processing with respect to the overlap areas.
On the other hand, a projector may not be able to be arranged in front of a screen due to the restriction of its setting place or location. In this case, a geometric distortion called a trapezoidal distortion may be caused to the projected images on the screen due to a relative tilt of a main body of the projector with respect to the screen.
Accordingly, there is a projector which has a trapezoidal correction function to correct such a trapezoidal distortion by means of image processing. For example, in Japanese patent application laid-open No. 2005-123669, there is described in detail a calculation method for trapezoidal correction (keystone correction) based on a relative tilt angle between one projector main body and a screen.
In carrying out multiple projections, it is necessary to make the trapezoidal correction and the accurate alignment of the overlap areas compatible with each other, and hence, the operations of the installation or arrangement of the projector main body and the setting for the trapezoidal correction become complicated. In the case of a projector which does not have a lens shift function, it is necessary to move the projector main body for the alignment of the overlap areas, but the relative position of the projector with respect to the screen is changed due to such a movement, thus making it necessary to set the trapezoidal correction again. For that reason, it is necessary to carry out the adjustment or alignment of the projector main body and the trapezoidal correction in a repeated manner.
In addition, in Japanese patent application laid-open No. 2009-200613, there is proposed a method in which trapezoidal correction is carried out by aligning four corners of a projected image of each projector to the ends or corners of a rectangular screen at the time of multiple projection, and the adjustment or alignment of overlap areas of projected images is carried out by overlapping guides displayed in the overlap areas of individual projectors with one another.